Vertebral Column • Curved stack of 33 vertebrate divided into Chapter 9 5 regions • Cerivcal Region – 7 Biomechanics of the Human Spine • Thoracic Region – 12 • Lumbar Region – 5 • Sacrum – 5 fused • Coccyx – 4 fused Motion Segment Vertebral Joints • 2 adjacent vertebrae and the associated soft tissues • Functional unit of the • Anterior spine – intervertebral symphysis joints • Posterior – Gliding diarthrodial facet joints Facet Joint Functions Intervertebral Discs • Channel and limit ROM in the different regions of • Fibrocartilaginous discs that cushion the anterior the spine spinal symphysis joints • Assist in lad bearing, sustaining up to 30% of the • Composed of a nucleus pulposus surrounded by compressive load on the spine the annulus fibrosus – Especially in hyperextension 1 Spinal Curves Spinal Movements • All three planes • circumduction • Lordosis – Exaggerated lumbar curve • Kyphosis – Exaggerated thoracic curve • Scoliosis – Lateral spinal curvature Cervical Flexors Abdominal Flexors • Rectus capitus anterior • Rectus abdominis • Rectus capitis lateralis • Internal obliques • Longus capitis • External obliques • Longus colli • 8 pairs of hyoid muscles Cervical Extension Thoracic/Lumbar Extensors • Erector Spinae • Splenius capitis – Iliocostalis – Longissimus – Spinalis • Splenius cervicis • Semispinalis – Capitis – Cervicis • Assisted by: – Thoracis – Rectus capitis • Deep Spinal Muscles posterior major/minor – Multifidi – Obliques capitis – Rotatores – Interspinales superior/inferior – Intertransversarii – Levatores cotarum 2 Lateral Cervical Flexors Lateral Lumbar Flexors • Sternocleidomastoid • Quadratus Lumborum • Levator scapulae • Psoas Major • Scalenus – Anterior • Lumbar – Posterior Flexors/Extensors – Medius – unilaterally • Cervical flexors/extensors – Unilaterally Forces Acting on the Spine Anatomical Load • Body Weight • Body weight acts anterior to the spine • Ligament Tension – Causing forward bending • Muscle Tension (moment) • External loads Spinal Loading Lifting Loads • Because the spine is curved, body weight, acting • Compression vertically, has components of both compression (F C) • Anterior Shear and shear (F S) at most motion segments. 3 Lumbar Hyperextension Lumbar Hyperextension • Produces compressive forces on facet joints • Supporting up to 30% of force • Bending load (moment) in posterior direction • Anterior Tension • Posterior Compression Spinal Rotation • Generates shear stress in the intervertebral discs 4.